                               DRI User Guide

                           Precision Insight, Inc.

                                 18 May 2000

1.  Preamble

1.1  Copyright

Copyright © 2000 by Precision Insight, Inc., Cedar Park, Texas.  All Rights
Reserved.

Permission is granted to make and distribute verbatim copies of this document
provided the copyright notice and this permission notice are preserved on all
copies.

1.2  Trademarks

OpenGL is a registered trademark and SGI is a trademark of Silicon Graphics,
Inc.  Unix is a registered trademark of The Open Group.  The `X' device and X
Window System are trademarks of The Open Group.  XFree86 is a trademark of
The XFree86 Project.  Linux is a registered trademark of Linus Torvalds.
Intel is a registered trademark of Intel Corporation.  3Dlabs, GLINT, and
Oxygen are either registered trademarks or trademarks of 3Dlabs Inc. Ltd.
3dfx, Voodoo3, Voodoo4, and Voodoo5 are registered trademarks of 3dfx Inter-
active, Incorporated.  Matrox is a registered trademark of Matrox Electronic
Systems Ltd.  ATI Rage is a registered trademark of ATI Technologies, Inc.
All other trademarks mentioned are the property of their respective owners.

2.  Introduction

With XFree86 4.0 and Precision Insight's Direct Rendering Interface (DRI),
hardware accelerated 3D graphics can be considered a standard feature on
Linux workstations.  Support for other operating systems, such as FreeBSD, is
underway.

This document describes how to use the DRI system and troubleshoot problems
which may occur.  Readers should have a basic understanding of Linux, X and
OpenGL.  See the resources section at the end for more documentation and
software downloads.

This document does not cover compilation or installation of XFree86 4.0.  It
is assumed that you've already installed a Linux distribution which includes
XFree86 4.0 or that you're an experienced Linux developer who has compiled
the DRI for himself.  DRI download, compilation and installation instructions
can be found at http://dri.sourceforge.net/DRIcompile.html

3.  Supported Hardware

3D acceleration is currently only available for systems with Intel-compatible
CPUs.  Support for Alpha, and perhaps other CPUs, should be available in the
future.

XFree86 4.0 (or later versions) includes 3D acceleration for the following
graphics hardware:

   o 3dfx:

        o Voodoo3 3500 TV

        o Voodoo3 3000 AGP

        o Voodoo3 3000 PCI

        o Voodoo3 2000 AGP

        o Voodoo3 2000 PCI

        o Voodoo Banshee

        o Velocity 100/200

     There are many configurations of 3dfx cards on the market.  Not all have
     been tested.

   o Matrox:

        o Matrox G200

        o Matrox G400

   o Intel i810

        o i810

        o i810-dc100

        o i810e

   o ATI Rage 128

        o Rage Fury AGP

        o Rage Magnum AGP

        o XPERT 2000 AGP

        o XPERT 128 AGP

        o XPERT 99 AGP

        o All-in-Wonder 128 AGP

     The PCI versions of these cards also have minimal support.  Note that
     there are also Rage 128 Pro based boards on the market, and these are
     not yet supported.

   o 3Dlabs Oxygen GMX 2000 (MX/Gamma based)

Support for the following hardware is underway:

   o 3dfx Voodoo4 and Voodoo5 series

4.  Prerequisite Software

   o XFree86 4.0

   o For the 3dfx Voodoo3 driver, Linux kernel 2.2.x (later kernels will be
     supported in the near future, and may be required for some chipsets)

   o For the Matrox G200/G400, Linux kernel 2.3.51, with AGP support

   o For the Intel i810, Linux kernel 2.3.99-pre6, with AGP support

Mesa 3.3 (beta) is included with XFree86 4.0; there is no need to download
the stand-alone Mesa distribution.

5.  X Server Start-up

This section describes the steps needed to start the X server with 3D accel-
eration support.

5.1  Kernel module

XFree86 4.0.1 added automatic kernel module loading to the X server.  On
Linux, the X server uses modprobe to load kernel modules.  The DRM kernel
modules should be in /lib/modules/KERNEL-VERSION/misc/ for automatic loading
to work.

Optionally, DRM kernel modules can be loaded manually with insmod prior to
starting the X server.

You can verify that the kernel module was installed with lsmod, checking the
X server startup log, and checking that /proc/dri/0 exists.

5.2  XF86Config file

First, the XF86Config file must load the GLX and DRI modules:

          Section "Module"
          ...
          # This loads the GLX module
              Load       "glx"
          # This loads the DRI module
              Load       "dri"
          EndSection

Next, the DRI section can be used to restrict access to direct rendering.

If you want all of the users on your system to be able to use direct-render-
ing, then use a simple DRI section:

          Section "DRI"
               Mode 0666
          EndSection

This section will allow any user with a current connection to the X server to
use direct rendering.

If you want to restrict the use of direct-rendering to a certain group of
users, then create a group for those users by editing the /etc/group file on
your system.  For example, you may want to create a group called xf86dri and
place two users (e.g., fred and jane) in that group.  To do that, you might
add the following line to /etc/group:

             xf86dri:x:8000:fred,jane

You have to be careful that the group id (8000 in this example) is unique.

Then you would use the following DRI section:

             Section "DRI"
                  Group "xf86dri"
                  Mode 0660
             EndSection

This would limit access to direct-rendering to those users in the xf86dri
group (fred and jane in this example).  When other users tried to use direct
rendering, they would fall back to unaccelerated indirect rendering.

[Note that there is a known bug in XFree86 4.0 that prevents some changes to
the DRI section from taking effect.  Until this bug is fixed, if you change
the DRI section, please also remove the /dev/dri directory with the rm -rf
/dev/dri command.]

Next, the Device section of the XF86Config file must describe your particular
hardware.

For example, here's the Device section for a 3dfx Voodoo3 card:

             Section "Device"
                 Identifier  "Voodoo3"
                 VendorName  "3dfx"
                 Driver      "tdfx"
             EndSection

Here's the Device section for a Matrox G400 card:

          Section "Device"
              Identifier  "G400"
              VendorName  "Matrox"
              Driver      "mga"
              VideoRam    32768
          EndSection

Here's the Device section for an ATI Rage 128 card:

          Section "Device"
              Identifier  "Rage128"
              VendorName  "ATI"
              Driver      "r128"
          EndSection

Here's the Device section for an Intel i810 motherboard:

          Section "Device"
              Identifier  "i810"
              VendorName  "Intel"
              Driver      "i810"
              VideoRam    10000
          EndSection

Finally, the Screen section of the XF86Config file may have to be specially
configured as well.  For example, Voodoo3 hardware acceleration is only
available in 16bpp mode.

          Section "Screen"
              Identifier  "Screen 1"
              Device      "Voodoo3"
              Monitor     "High Res Monitor"
              DefaultDepth 16
              Subsection "Display"
               Depth       16
               Modes       "1280x1024" "1024x768" "800x600" "640x480"
               ViewPort    0 0
              EndSubsection
             EndSection

Replace Voodoo3 with G400 for Matrox G400.

Replace Voodoo3 with Rage128 for ATI Rage 128.

If there are errors in the XF86Config file, the X server will log errors to
the file /var/log/XFree86.0.log

5.3  Memory usage

Using the 3D features of a graphics card requires more memory than when it's
just used as a 2D device.  Double buffering, depth buffering, stencil
buffers, textures, etc. all require extra graphics memory.  These features
may require four times the memory used for a simple 2D display.

If your graphics card doesn't have a lot of memory (less than 16MB, for exam-
ple), you may have to reduce your screen size and/or color depth in order to
use 3D features.

The documentation included with your card should have information about maxi-
mum screen size when using 3D.

6.  Using 3D Acceleration

This section describes how to link your application with libGL.so and verify
that you are in fact using 3D acceleration.

6.1  libGL.so

Your OpenGL program must link with the libGL.so.1.2 library provided by
XFree86 4.0.  The libGL.so.1.2 library contains a GLX protocol encoder for
indirect/remote rendering and DRI code for accessing hardware drivers.  In
particular, be sure you're not using libGL.so from another source such as
Mesa or the Utah GLX project.

Unless it was built in a special way, the libGL.so library does not contain
any 3D hardware driver code.  Instead, libGL.so dynamically loads the appro-
priate 3D driver during initialization.

Most simple OpenGL programs also use the GLUT and GLU libraries.  A source
for these libraries is listed in the Resources section below.

6.2  Compiling and linking an OpenGL program

A simple GLUT/OpenGL program may be compiled and linked as follows:

             gcc program.c -I/usr/local/include -L/usr/local/lib -L/usr/X11R6/lib -lglut -lGLU -lGL -o program

The -I option is used to specify where the GL/glut.h (and possibly the
GL/gl.h and GL/glu.h) header file may be found.

The -L options specify where the libglut.so, libGLU.so and X libraries are
located.

The -lglut -lGLU -lGL arguments specify that the application should link with
the GLUT, GLU and GL libraries.

6.3  Running your OpenGL program

Simply typing ./program in your shell should execute the program.

If you get an error message such as

             gears: error in loading shared libraries: libGL.so.1: cannot
             open shared object file: No such file or directory

if means that the libGL.so.1 file is not the right location.  Proceed to the
trouble shooting section.

6.4  libOSMesa.so

OSMesa (Off-Screen Mesa) is an interface and driver for rendering 3D images
into a user-allocated block of memory rather than an on-screen window.

libOSMesa.so implements the OSMesa interface and must be linked with your
application if you want to use the OSMesa functions.  You must also link with
libGL.so.  For example:

             gcc osdemo.c -L/usr/X11R6/lib -lOSMesa -lGLU -lGL -o osdemo

In stand-alone Mesa this interface was compiled into the monolithic libGL.so
(formerly libMesaGL.so) library.  In XFree86 4.0.1 and later this interface
is implemented in a separate library.

6.5  glxinfo

glxinfo is a useful program for checking which version of libGL you're using
as well as which DRI-based driver.  Simply type glxinfo and examine the
OpenGL vendor, renderer, and version lines.  Among the output you should see
something like this:

               OpenGL vendor string: Precision Insight, Inc.
               OpenGL renderer string: Mesa DRI Voodoo3 20000224
               OpenGL version string: 1.2 Mesa 3.3 beta

or this:

               OpenGL vendor string: Precision Insight, Inc.
               OpenGL renderer string: Mesa GLX Indirect
               OpenGL version string: 1.2 Mesa 3.3 beta

The first example indicates that the 3dfx driver is using Voodoo3 hardware.
The second example indicates that no hardware driver was found and indirect,
unaccelerated rendering is being used.

If you see that indirect rendering is being used when direct rendering was
expected, proceed to the troubleshooting section.

glxinfo also lists all of the GLX-enhanced visuals available.  Here you can
determine which visuals may have depth buffers, stencil buffers, accumulation
buffers, etc.

6.6  Environment Variables

The libGL.so library recognizes three environment variables.  Normally, none
of them need to be defined.  If you're using the csh or tcsh shells, type
setenv VARNAME value to set the variable.  Otherwise, if you're using sh or
bash, type export VARNAME=value.

  1.  LIBGL_DEBUG, if defined will cause libGL.so to print error and diagnos-
      tic messages.  This can help to solve problems.  Setting LIBGL_DEBUG to
      verbose may provide additional information.

  2.  LIBGL_ALWAYS_INDIRECT, if defined this will force libGL.so to always
      use indirect rendering instead of hardware acceleration.  This can be
      useful to isolate rendering errors.

  3.  LIBGL_DRIVERS_PATH can be used to override the default directories
      which are searched for 3D drivers.  The value is one or more paths sep-
      arated by colons.  In a typical XFree86 installation, the 3D drivers
      should be in /usr/X11R6/lib/modules/dri/ and LIBGL_DRIVERS_PATH need
      not be defined.  Note that this feature is disabled for set-uid pro-
      grams.  This variable replaces the LIBGL_DRIVERS_DIR env var used in
      XFree86 4.0.

Mesa-based drivers (this includes most of the drivers listed above) also
observe many of the existing Mesa environment variables.  These include the
MESA_DEBUG and MESA_INFO variables.

7.  General Trouble Shooting

This section contains information to help you diagnose general problems.  See
below for additional information for specific hardware.

7.1  Starting the X server

  1.  Before you start the X server, verify the appropriate 3D kernel module
      is installed.  Type lsmod and look for the appropriate kernel module.
      For 3dfx hardware you should see tdfx, for example.

  2.  Verify you're running XFree86 4.0 and not an older version.  If you run
      xdpyinfo and look for the following line near the top:

                       vendor release number:    4000

  3.  Verify that your XF86Config file (usually found at /etc/X11/XF86Config)
      loads the glx and dri modules and has a DRI section.

      See the Software Resources section below for sample XF86Config files.

  4.  Examine the messages printed during X server startup and check that the
      DRM module loaded.  Using the Voodoo3 as an example:

                   (==) TDFX(0): Write-combining range (0xf0000000,0x2000000)
                   (II) TDFX(0): Textures Memory 7.93 MB
                   (0): [drm] created "tdfx" driver at busid "PCI:1:0:0"
                   (0): [drm] added 4096 byte SAREA at 0xc65dd000
                   (0): [drm] mapped SAREA 0xc65dd000 to 0x40013000
                   (0): [drm] framebuffer handle = 0xf0000000
                   (0): [drm] added 1 reserved context for kernel
                   (II) TDFX(0): [drm] Registers = 0xfc000000
                   (II) TDFX(0): visual configs initialized
                   (II) TDFX(0): Using XFree86 Acceleration Architecture (XAA)
                           Screen to screen bit blits
                           Solid filled rectangles
                           8x8 mono pattern filled rectangles
                           Indirect CPU to Screen color expansion
                           Solid Lines
                           Dashed Lines
                           Offscreen Pixmaps
                           Driver provided NonTEGlyphRenderer replacement
                           Setting up tile and stipple cache:
                                   10 128x128 slots
                   (==) TDFX(0): Backing store disabled
                   (==) TDFX(0): Silken mouse enabled
                   (0): X context handle = 0x00000001
                   (0): [drm] installed DRM signal handler
                   (0): [DRI] installation complete
                   (II) TDFX(0): direct rendering enabled

  5.  After the X server has started, verify that the required X server
      extensions are loaded.  Run xdpyinfo and look for the following entries
      in the extensions list:

                  GLX
                  SGI-GLX
                  XFree86-DRI

7.2  Linking, running and verifying 3D acceleration

After you've verified that the X server and DRI have started correctly it's
time to verify that the GL library and hardware drivers are working cor-
rectly.

  1.  Verify that you're using the correct libGL.so library with ldd.  The
      /usr/lib and /usr/X11R6/lib directories are expected locations for
      libGL.so.

      Example:

                   % ldd /usr/local/bin/glxinfo
                           libglut.so.3 => /usr/local/lib/libglut.so.3 (0x40019000)
                           libGLU.so.1 => /usr/local/lib/libGLU.so.1 (0x40051000)
                           libGL.so.1 => /usr/lib/libGL.so.1 (0x40076000)
                           libXmu.so.6 => /usr/X11R6/lib/libXmu.so.6 (0x402ee000)
                           libXi.so.6 => /usr/X11R6/lib/libXi.so.6 (0x40301000)
                           libm.so.6 => /lib/libm.so.6 (0x40309000)
                           libc.so.6 => /lib/libc.so.6 (0x40325000)
                           libX11.so.6 => /usr/X11R6/lib/libX11.so.6 (0x40419000)
                           libXt.so.6 => /usr/X11R6/lib/libXt.so.6 (0x404bd000)
                           libSM.so.6 => /usr/X11R6/lib/libSM.so.6 (0x40509000)
                           libICE.so.6 => /usr/X11R6/lib/libICE.so.6 (0x40512000)
                           libXext.so.6 => /usr/X11R6/lib/libXext.so.6 (0x40529000)
                           libvga.so.1 => /usr/lib/libvga.so.1 (0x40537000)
                           libpthread.so.0 => /lib/libpthread.so.0 (0x4057d000)
                           /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x40000000)

  2.  You may also double check that libGL.so is in fact DRI-capable.  Run
      strings libGL.so.1.2 | grep DRI and look for symbols prefixed with
      "XF86DRI", such as "XF86DRIQueryExtension".

  3.  To be safe one should run ldconfig after installing libGL.so to be sure
      the runtime loader will find the proper library.

  4.  Verify that the appropriate 3D driver is in /usr/X11R6/lib/modules/dri/
      For example, the 3dfx driver will be named tdfx_dri.so.

  5.  Set the LIBGL_DEBUG environment variable.  This will cause libGL.so to
      print an error message if it fails to load a DRI driver.  Any error
      message printed should be self-explanatory.

  6.  Run glxinfo.  Note the line labeled "OpenGL renderer string".  It
      should have a value which starts with "Mesa DRI" followed by the name
      of your hardware.

  7.  Older Linux OpenGL applications may have been linked against Mesa's GL
      library and will not automatically use libGL.so.  In some cases, making
      symbolic links from the Mesa GL library to libGL.so.1 will solve the
      problem:

                   ln -s libGL.so.1 libMesaGL.so.3

      In other cases, the application will have to be relinked against the
      new XFree86 libGL.so.

      It is reported that part of the problem is that running ldconfig will
      silently rewrite symbolic links based on the SONAME field in libraries.

If you're still having trouble, look in the next section for information spe-
cific to your graphics card.

8.  Hardware-Specific Information and Troubleshooting

This section presents hardware-specific information for normal use and trou-
bleshooting.

8.1  3dfx Voodoo3

8.1.1  Configuration

Your XF86Config file's device section must specify the tdfx device:

             Section "Device"
                 Identifier  "Voodoo3"
                 VendorName  "3dfx"
                 Driver      "tdfx"
             EndSection

The Screen section should then reference the Voodoo3 device:

          Section "Screen"
              Identifier  "Screen 1"
              Device      "Voodoo3"
              Monitor     "High Res Monitor"
              DefaultDepth 16
              Subsection "Display"
               Depth       16
               Modes       "1280x1024" "1024x768" "800x600" "640x480"
               ViewPort    0 0
              EndSubsection
             EndSection

The kernel module for the Voodoo3 is named tdfx.o and should be installed in
/lib/modules/KERNEL-VERSION/misc/.  It will be automatically loaded by the
Xserver if needed.

The DRI 3D driver for the Voodoo3 should be in /usr/X11R6/lib/mod-
ules/dri/tdfx_dri.so.  This will be automatically loaded by libGL.so.

8.1.2  Troubleshooting

   o 3D acceleration for Voodoo3 is only supported in the 16 bit/pixel screen
     mode.  Use xdpyinfo to verify that all your visuals are depth 16.  Edit
     your XF86Config file if needed.

   o The /dev/3dfx device is not used for DRI; it's only for Glide on older
     3dfx hardware.

8.1.3  Performance

   o Normally, buffer swapping in double-buffered applications is synchro-
     nized to your monitor's refresh rate.  This may be overridden by setting
     the FX_GLIDE_SWAPINTERNVAL environment variable.  The value of this
     variable indicates the maximum number of swap buffer commands can be
     buffered.  Zero allows maximum frame rate.

   o The glTexEnv mode GL_BLEND is not directly supported by the 3dfx hard-
     ware.  It can be accomplished with a multipass algorithm but it's not
     implemented at this time.  Applications which use that mode, such as the
     Performer Town demo, may become sluggish when falling back to software
     rendering to render in that mode.

8.1.4  Known Problems

   o Glide cannot be used directly; only OpenGL-based programs are supported
     on the Voodoo3.

   o SSystem has problems because of poorly set near and far clipping planes.
     The office.unc Performer model also suffers from this problem.

8.2  Intel i810

8.2.1  Configuration

Your XF86Config file's device section must specify the i810 device, and spec-
ify a usable amount of video ram to reserve.

             Section "Device"
                 Identifier  "i810"
                 VendorName  "Intel"
                 Driver      "i810"
              VideoRam    10000
             EndSection

The Screen section should then reference the i810 device:

          Section "Screen"
              Identifier  "Screen 1"
              Device      "i810"
              Monitor     "High Res Monitor"
              DefaultDepth 16
              Subsection "Display"
               Depth       16
               Modes       "1280x1024" "1024x768" "800x600" "640x480"
               ViewPort    0 0
              EndSubsection
             EndSection

The kernel module for the i810 is named i810.o and should be installed in
/lib/modules/KERNEL-VERSION/misc/.  It will be automatically loaded by the
Xserver if needed.

The DRI 3D driver for the i810 should be in /usr/X11R6/lib/mod-
ules/dri/i810_dri.so.  This will be automatically loaded by libGL.so.

8.2.2  Troubleshooting

   o 3D acceleration for the i810 is only available in the 16 bit/pixel
     screen mode at this time.  32bpp acceleration is not supported by this
     hardware.  Use xdpyinfo to verify that all your visuals are depth 16.
     Edit your XF86Config file if needed.

   o The i810 uses system ram for video and 3d graphics.  The X server will
     ordinarily reserve 4mb of ram for graphics, which is too little for an
     effective 3d setup.  To tell the driver to use a larger amount, specify
     a VideoRam option in the Device section of your XF86Config file.  A num-
     ber between 10000 and 16384 seems adequate for most requirements.  If
     too little memory is available for DMA buffers, back and depth buffers
     and textures, direct rendering will be disabled.

8.3  Matrox G200 and G400

8.3.1  Configuration

Your XF86Config file's device section must specify the mga device:

             Section "Device"
                 Identifier  "MGA"
                 VendorName  "Matrox"
                 Driver      "mga"
             EndSection

The Screen section should then reference the MGA device:

          Section "Screen"
              Identifier  "Screen 1"
              Device      "MGA"
              Monitor     "High Res Monitor"
              DefaultDepth 16
              Subsection "Display"
               Depth       16
               Modes       "1280x1024" "1024x768" "800x600" "640x480"
               ViewPort    0 0
              EndSubsection
             EndSection

The kernel module for the G200/G400 is named mga.o and should be installed in
/lib/modules/KERNEL-VERSION/misc/.  It will be automatically loaded by the
Xserver if needed.

The DRI 3D driver for the G200/G400 should be in /usr/X11R6/lib/mod-
ules/dri/mga_dri.so.  This will be automatically loaded by libGL.so.

8.3.2  Troubleshooting

   o 3D acceleration for the G200 and G400 is only supported in the 16
     bit/pixel screen mode at this time.  32bpp will be supported in the
     future.  Use xdpyinfo to verify that all your visuals are depth 16.
     Edit your XF86Config file if needed.

8.3.3  Performance

No data at this time.

8.3.4  Known Problems

   o Multitexture is currently disabled on the G400 to work around a hardware
     lockup bug.  This should be restored in a subsequent release.

8.4  ATI Rage 128

8.4.1  Configuration

Your XF86Config file's device section must specify the r128 device:

             Section "Device"
                 Identifier  "Rage128"
                 VendorName  "ATI"
                 Driver      "r128"
             EndSection

The Screen section should then reference the Rage 128 device:

          Section "Screen"
              Identifier  "Screen 1"
              Device      "Rage128"
              Monitor     "High Res Monitor"
              DefaultDepth 16
              Subsection "Display"
               Depth       16
               Modes       "1280x1024" "1024x768" "800x600" "640x480"
               ViewPort    0 0
              EndSubsection
              Subsection "Display"
               Depth       32
               Modes       "1280x1024" "1024x768" "800x600" "640x480"
               ViewPort    0 0
              EndSubsection
             EndSection

The kernel module for the Rage 128 is named r128.o and should be installed in
/lib/modules/KERNEL-VERSION/misc/.  It will be automatically loaded by the
Xserver if needed.

The DRI 3D driver for the Rage 128 should be in /usr/X11R6/lib/mod-
ules/dri/r128_dri.so.  This will be automatically loaded by libGL.so.

You may also set your screen depth to 32 for 32bpp mode.

8.4.2  Performance

While PCI Rage 128 based cards are supported, they do not yet support PCI
GART, so they will not perform as well as their AGP counterparts.

8.4.3  Known Problems

DGA is not yet supported in the ATI Rage 128 X server.  This feature will be
added in a future release.

8.5  3DLabs Oxygen GMX 2000

The driver for this hardware was experimental and is no longer being devel-
oped or supported.

9.  Limitations and Known Bugs

9.1  OpenGL

The following OpenGL features are not supported at this time: overlays,
stereo, hardware-accelerated indirect rendering.

OpenGL-like functionality is provided with the Mesa library.  XFree86 4.0
uses a beta version Mesa 3.3.  When newer versions of Mesa are available, the
3D drivers can be updated without reinstalling XFree86 or libGL.so.

9.2  GLX

The GLX 1.3 API is exported but none of the new 1.3 functions are opera-
tional.

The new glXGetProcAddressARB function is fully supported.

9.3  Signal Handling

There are several understood, but unresolved problems relating to hardware
locking and signal handling.  Hitting CTRL-z to suspend a 3D application can
sometimes cause the X server to lock-up if executing device driver code at
that moment.  Also, using a debugger to step through OpenGL/Mesa device
driver functions code could cause a lock-up.  These problems will be fixed in
the future.

9.4  Scheduling

When you run multiple GL applications at once you may notice poor time slic-
ing.  This is due to an interaction problem with the Linux scheduler which
will be addressed in the future.

9.5  libGL.so and dlopen()

A number of popular OpenGL applications on Linux (such as Quake3, HereticII,
Heavy Gear 2, etc) dynamically open the libGL.so library at runtime with
dlopen(), rather than linking with -lGL at compile/link time.

If dynamic loading of libGL.so is not implemented carefully, there can be a
number of serious problems.  Here are the things to be careful of in your
application:

   o Specify the RTLD_GLOBAL flag to dlopen().  If you don't do this then
     you'll likely see a runtime error message complaining that _glapi_Con-
     text is undefined when libGL.so tries to open a hardware-specific
     driver.  Without this flag, nested opening of dynamic libraries does not
     work.

   o Do not close the library with dlclose() until after XCloseDisplay() has
     been called.  When libGL.so initializes itself it registers several
     callbacks functions with Xlib.  When XCloseDisplay() is called those
     callback functions are called.  If libGL.so has already been unloaded
     with dlclose() this will cause a segmentation fault.

   o Your application should link with -lpthread.  On Linux, libGL.so uses
     the pthreads library in order to provide thread safety.  There is appar-
     ently a bug in the dlopen()/dlclose() code which causes crashes if the
     library uses pthreads but the parent application doesn't.  The only
     known work-around is to link the application with -lpthread.

Some applications don't yet incorporate these procedures and may fail.  For
example, changing the graphics settings in some video games will expose this
problem.  The DRI developers are working with game vendors to prevent this
problem in the future.

9.6  Bug Database

The DRI bug database which includes bugs related to specific drivers is at
the SourceForge DRI Bug Database

Please scan both the open and closed bug lists to determine if your problem
has already been reported and perhaps fixed.

10.  Resources

10.1  Software

A collection of useful configuration files, libraries, headers, utilities and
demo programs is available from http://dri.source-
forge.net/resources/resources.html

10.2  Documentation

   o General OpenGL information is available at the OpenGL Home Page

   o XFree86 information is available at the XFree86 Home Page

   o Information about the design of the DRI is available from Precision
     Insight, Inc.

   o Visit the DRI project on SourceForge.net for the latest development news
     about the DRI and 3D drivers.

   o The DRI Compilation Guide explains how to download, compile and install
     the DRI for yourself.

10.3  Support

   o The DRI-users mailing list at SourceForge is a forum for people to dis-
     cuss DRI problems.

   o In the future there may be IHV and Linux vendor support resources for
     the DRI.

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